Catalytic nanoparticles can make up the active sites of catalysts used in a variety of applications, such as for the production of fuels, chemicals and pharmaceuticals, and for emissions control from automobiles, factories, and power plants. Because catalytic nanoparticles tend to agglomerate, this decreases their surface area and active site accessibility, so they are often coupled to support materials. The supports physically separate the catalytic nanoparticles to prevent agglomeration, and to increase their surface area and active site accessibility. Thus, catalyst systems typically include one or more compounds; a porous catalyst support material; and one or more optional activators.
After continued use, especially at elevated temperatures, catalyst systems comprising supported catalytic nanoparticles lose catalytic activity due to sintering, e.g., thermal deactivation that occurs at high temperatures. Through various mechanisms, sintering results in changes in metal particle size distribution over a support and an increase in mean particle size; hence, a decrease in surface area for the active catalyst compounds. For example, particle migration and coalescence is a form of sintering where particles of catalytic nanoparticles move or diffuse across a support surface, or through a vapor phase, and coalesce with another nanoparticle, leading to nanoparticle growth. Ostwald ripening is another form of sintering wherein migration of mobile species are driven by differences in free energy and local atom concentrations on a support surface. After sintering processes occur, catalyst activity can decrease. Therefore, catalyst systems are often loaded with a sufficient amount of supported catalytic nanoparticles to account for a loss of catalytic activity over time and to continue to have the ability to meet, for example, emissions standards over a long period of operation at high temperature.